Conventionally, polycarbonate resins reinforced with carbon fibers have various excellent performances, but have a disadvantage that deposits tend to adhere to a mold at molding thereof. In particular, in the case that the mold structure is complicated, e.g., in the production of precision machinery parts, this tendency is strong Therefore, disassembly and cleaning of the mold are required, and continuous molding operation over a long period of time is impossible.
As a result of investigating the cause of such mold deposit, it was found that an epoxy resin, a urethane resin or other resin used as a sizing agent for carbon fibers decomposes or volatilizes during molding to adhere to the mold, causing the mold deposit.
In general, several thousand carbon fiber monofilaments are bundled, and a sizing agent for carbon fibers is applied thereto in an amount of 2.5 to 7.0% by weight, followed by drying to fix the agent. If the amount of the sizing agent applied is below 2.5% by weight, the carbon fibers desize to form pills at the time of mixing thereof with a polycarbonate resin, so that the extrusion workability of the resulting composition becomes extremely poor. On the other hand, if the amount of the sizing agent exceeds 7.0% by weight, the dispersibility of the carbon fibers into a polycarbonate resin becomes so poor that the resulting composition gives extrudates having poor appearance, although the mixing and extruding operations per se can be satisfactorily conducted. The amount of the sizing agent applied is determined from the balance between workability and dispersibility, but this sizing agent is the cause of the mold deposit.
Therefore, a carbon fiber-reinforced polycarbonate resin composition which satisfies both the workability and appearance requirements and causes no mold deposit has been strongly demanded.